NAPLES - "Nobody knows what's causing the drop," Collier County Sheriff Kevin Rambosk said. "I would love to be able to tell you I know the answer to that. I don't. But I know what has worked well for us."

In the past 15 years, most of Collier County's decline in its crime rate has been the result of fewer nonviolent crimes -- burglary, larceny and motor vehicle theft.

Collier.....1996......2010

Murder......4.............11

Rape.......136.........117

Robbery...303........204

Assault....889.........752

Burglary..2,740....1,199

Larceny...6,972....4,344

Auto theft...726.....196

For the past 15 years, as Collier County underwent one of the most volatile times in its history — a population boom, a real estate market bust, unstable employment rates — one trend has remained the same.

Crime fell.

The rate of crimes judged most serious by the FBI, called Part I crimes, has dropped each year in Collier County for the past decade and a half, a review of data submitted annually to the Florida Department of Law Enforcement shows.

During that time, Collier County was the state's only county to see a drop every year. In all, the Part I crime rate fell by 66 percent between 1996 and 2010.

The decline reflects the national fall-off in reported crime, a trend that has baffled law enforcement.

"Nobody knows what's causing the drop," Collier County Sheriff Kevin Rambosk said. "I would love to be able to tell you I know the answer to that. I don't. But I know what has worked well for us."

Local law enforcement administrators and criminal justice professors offer theories about what's caused the Collier crime rate drop — an aging population, more affluent residents migrating here and law enforcement working more efficiently.

But scientifically, nobody knows for sure.

"When you're predicting human behaviors, there are so many variables that we can't measure or don't know about," said Mary Ann Zager, chairwoman of the Division of Justice Studies at Florida Gulf Coast University. "It does make it a little bit of an educated guess in the end."

Which begs fundamental questions about crime: How do we measure it? What causes it to rise or fall? And how do police decipher which tactics work, and which don't?

'A pretty good indicator'

Each year, Collier County law enforcement agencies submit data to the FBI called a Uniform Crime Report, which measures the number of reported crimes in their jurisdiction. The most frequently cited statistic is Part I crimes — homicide, rape, robbery, aggravated assault, burglary, larceny and motor vehicle theft.

Since 1996, the annual decline in Collier County's Part I crime rate has ranged from 1 percent in 2008 to 17 percent in 2000. In those 15 years overall, the rate has fallen from about 6,100 per 100,000 residents to 2,040 per 100,000 residents.

Three criminal justice experts contacted by the Daily News reviewed the Collier data and were in agreement: although the actual number of crimes might not have dropped, the gradual decline suggests the county has become a safer place since the mid-1990s.

"Those figures are not exact or without error, so I wouldn't say that they precisely represent the changes in crime, but they're all negative and I think that's a pretty good indicator," said Ken Adams, a University of Central Florida criminal justice professor.

Since 1996, the annual decline in Collier County's Part I crime rate has ranged from 1 percent in 2008 to 17 percent in 2000. In those 15 years overall, the rate has fallen from about 6,100 per 100,000 residents to 2,040 per 100,000 residents.

Nationally, Part I offenses have fallen 34 percent between 1996 and 2010. In Florida, it's been 45 percent during the same time period.

What makes Collier County unique: No other county has had such consistent declines (Hillsborough County has the second-longest active streak of annual reductions at eight). And while the FBI advises against comparing jurisdictions, it's worth nothing that only Liberty County, the state's least-populous county, has seen a greater drop.

An imperfect process

There are, however, flaws with the Uniform Crime Report data.

Crimes that go unreported to police aren't counted. In a case involving multiple crimes, only the most serious one is documented in Uniform Crime Report data.

Some areas have been found to manipulate statistics to keep rates low, though local officials say that doesn't happen here.

Perhaps most notably, the Part I crime rate frequently cited doesn't weigh the seriousness of a crime. A murder counts the same as a larceny in the total crime rate, for example.

In Collier County, most of the crime rate drop can be attributed to fewer nonviolent Uniform Crime Report offenses — burglary, larceny and motor vehicle theft. Those offenses, which make up 80 percent to 90 percent of Part I crimes, have fallen by 45 percent since 1996. During the same time period, violent crimes reported — homicide, rape, robbery and aggravated assault — dropped by 25 percent.

Still, most criminologists agree the crime report data gives the best picture of crime in an area.

"For what they measure, I personally believe the Uniform Crime Report is the most reliable and valid data in the world," FGCU's Zager said.

The question then becomes: Why has crime fallen?

A case of demographics

Considering Collier County's head count rose from 193,000 in 1996 to 331,400 according to current estimates, the starting point is population makeup, professors said.

While the census, taken every 10 years, doesn't provide a snapshot of the county in 1996, some trends come to light from the surveys taken in 2000 and 2010.

During the decade, the county aged slightly, with the percentage of the population age 60 and over rising from 31 percent to 33.7 percent. The age group generally considered to commit the most Part I crimes — those between ages 15 and 34 — now makes up 1 percent less of the population.

The racial makeup has changed more drastically. Whites account for 8 percent less of the population in 2010 compared with 2000. That difference is made up primarily by Latinos (up 6.3 percent) and blacks (up 1.6 percent).

During the decade, the county aged slightly, with the percentage of the population age 60 and over rising from 31 percent to 33.7 percent. The age group generally considered to commit the most Part I crimes — those between ages 15 and 34 — now makes up 1 percent less of the population.

More local students are receiving high school and college degrees. Residents also have more money now, with median household income up about $10,000 per year. But the changes for both are no better than national averages.

One common myth that has been shot down, both nationally and locally: higher unemployment means more crime.

"It's not that people lose their jobs and then those people go out and commit crime," Zager said.

Of the major demographic indicators — age, race, education, income, employment status — only the increase in the Latino population stands out.

Adams, the UCF professor, said the demographic trends in Collier County run counter to traditional theories of criminal activity.

"When you've got large increases in population and large increases in minorities, you would expect the crime rate to go up, but it's definitely going down," Adams said.

Police response

With demographics not providing any obvious reasons, the focus turns to local law enforcement.

Both Collier County sheriffs during the 15-year run said several changes have made law enforcement better and more efficient.

Don Hunter, sheriff until 2008 and Marco Island's current police chief, said a focus on career criminals helped. Deputies were directed to keep tabs on gang members, those with arrest warrants and residents with multiple convictions, Hunter said.

"A very small percentage of the criminal population — 8 (percent) to 10 percent — are committing 80 (percent) to 90 percent of the crimes," former Collier Sheriff Don Hunter said.

"A very small percentage of the criminal population — 8 (percent) to 10 percent — are committing 80 (percent) to 90 percent of the crimes," Hunter said.

Although some scholars have called community policing a hollow buzzword, current sheriff Rambosk said the system has brought crime down since it started in the mid-1990s under Hunter.

"Historically, up to that point, everybody worked rotating shifts," Rambosk said. "Nobody spent a lot of time learning the neighborhoods."

In-car work stations also keep deputies on the street more, which some researchers suggest is a deterrent. The introduction of CompStat, a computer system that maps crime trends, in 1999 also has helped administrators develop target areas for enforcement.

"Essentially we're looking at what has occurred, what could occur, and who might be involved in committing future crimes," Rambosk said. "That enables us to focus on areas that we think might be a problem, and that goes to prevention."

Hunter credits a fourth factor: a push started in 2007 to deport illegal immigrants arrested by deputies. A 2007 snapshot found about a quarter of jail inmates were self-admitted illegal immigrants.

The budget response

The downturn in crime hasn't run parallel to funding, raising the question of whether more law enforcement money means lower crime rates.

Between 2002 and 2007, the Sheriff's Office saw its budget rise by at least 11 percent each year. Since 2009, the budget has been cut by 1 percent to 5 percent annually, down to about $132 million this fiscal year.

Between 2002 and 2007, the Sheriff's Office saw its budget rise by at least 11 percent each year. Since 2009, the budget has been cut by 1 percent to 5 percent annually, down to about $132 million this fiscal year.

Yet both local officials and criminal justice scholars advise against tying crime rates to budgeting levels, saying Part I crime response is one of many responsibilities of law enforcement.

"The things you should be looking at that aren't as sexy or exciting are the regular quality of life issues," said Rosemary Arway, a Hodges University criminal justice professor. "Some of the smaller things — domestic violence, things you see with the economy, alcohol-related incidents, drug usage — aren't the things that get attention."

There are indicators that crime rates have hit a valley. Part I crimes in Collier County rose 6 percent in the first half of 2011 when compared to the same time period in 2010.

Rambosk offered several reasons for the early jump in 2011: the growing illegal prescription pill market, more criminals coming from Florida's east coast and the down economy.

But like the reasons offered for the 15-year decline, it's difficult to prove the scientific validity of these explanations.

"I think our dilemma is that while we track everything we know or can think of that might help us stop the potential for crime, it can only go so low," Rambosk said. "Although I'd like none, it's more challenging to a degree being low. We're trying to find out in a county of 2,000 square miles where the potential next crime is going to be."

* * * * *

Each year, Florida's policing agencies count the number of reported crimes in their areas. The most commonly cited statistic is the rate of Part I crimes -- homicide, rape, robbery, aggravated assault, burglary, larceny and motor vehicle theft -- per 100,000 residents. Here's how Collier County's Part I crime rate compares to Lee County and the state during that time.